Today, with advancement of the information-oriented society, an amount of information being processed by computers has increased. Correspondingly it is strongly required to increase the storage capacity of a magnetic disk device, and a successive improvement of recording density is indispensable.
To increase the recording density of a magnetic disk device, it is important to improve a performance of a read/write channel along with an improving performance of components such as a magnetic head and a magnetic disk medium. Especially, in recent years, the PRML method has been employed in the reproducing channel and performance of discriminating data from a low S/N reproduced signal has been improved. In this PRML method, interference between the front part and rear part of a reproduced signal is used effectively, therefore it is necessary to equalize the reproduced signal wave to an ideal wave form and obtain proper interference of the wave form. When an equalization error is considerable, a discrimination error occurs easily and reproduction of recorded data may not be executed normally. Therefore, the wave equalization technology is especially important. Further, this wave equalization technology is important also in an improved PRML method.
Accordingly, when a variation of the reproduced signal wave form is caused by a variation in characteristics of a magnetic head or magnetic disk medium, etc., the adaptive equalization technology is combined in order to equalize the reproduced signal wave form to the ideal wave form.
In the usual adaptive equalization as shown in FIG. 1, an equalization error at each sampling point on the reproduced signal wave form is evaluated, and a value of equalization coefficient at each tap of a transversal equalizer is learned and applied so as to minimize the equalization error. Further, in order to absorb a deviation of synchronization timing in a read operation caused by a variation of the read/write channel IC, various kinds of methods for automatic adaptation functions of parameters have also been applied. These technologies recently have advanced and have been applied rapidly to a wide range of digital technology fields.
A technology in that parameters are automatically adjusted with a constant time interval specified in advance instead of at each read operation, is disclosed in Japanese patent unexamined publication Hei 8-293165 (patent application Hei 7-96820).
This automatic adaptation of coefficient for equalization is started at the same time that reproducing data is started as shown in FIG. 2. Namely, automatic adaptation of the equalization coefficient is executed using a signal wave received in a read-gate timing. Therefore, when the device has just started, or when some long time has passed after the previous adaptation, coefficients for equalization are not fully adapted or adapted insufficiently.
When the equalization coefficients before being adapted have inadequate values, there is a possibility of making some troubles such that a long time is required for adaptation or the read operation is abortive at the beginning of reading data. Therefore, it is required that the equalization coefficients are to be set to the adequate initial constants at the beginning of automatic adaptation. The initial constants are learned at a shipment of the device and are recorded on the management information area in which the initial values of various parameters on the disk device are stored.
Coefficients for equalization are varied corresponding to a variation of characteristics of magnetic heads and magnetic disk media, and the initial constants are to be set for each head. Furthermore, recently, the magnetic disk has a constitution in which the disk medium is divided into plural zones radially and recording densities are optimized for each zone. Therefore, the initial constants are required to be set for each zone.
The above-mentioned initial constants are applied as equalization coefficients to a signal processing circuit that processes first read-out data just after the device has been started, after a head has been switched to another, or after a zone has been changed.
In conventional technologies as described above, in order to keep parameters such as coefficients for equalization as adequate as possible, the parameters learned at the shipment of the device are applied to. However, when an environment in real use differs seriously from one environment at the initial learning to another, the reproduced wave form is more varied from the original one, the equalization error becomes large, and the read error occurs easily at the data-read operation. This phenomenon makes the magnetic disk device seem to be deteriorated in performance. However, even in this environment, if the coefficient for equalization is learned again, it is often possible to read the data normally.
As described above, the purpose of the present invention is to provide a magnetic disk device in which a deterioration of performance caused by environmental variation is suppressed to the utmost.